What two ions are central to the arrhenius definitions of acids and bases?

hydrogen (H⁺) or hydronium (H₃O⁺) and hydroxide (OH⁻)

Explanation:

1) Arrhenius definitions

The chemist Svante Arrhenius, winner of the Noble Prize in chemistry by 1903, defined acids and bases based on the ability of such substances to give ions in water solutons.

2) Acids

Arrhenius defined an acid as a substance that dissociates in water to form hydrogen ions (H⁺), also called protons. This process is called protonation (formation of protons). Due to its small size and high activity, H⁺ does not exist in that form, but it forms H₃O⁺ ions in aqueous solution.

3) Bases

Arrhenius defined a base as a substance that dissociates in water to form hydroxide (OH⁻) ions.

4) Examples

That was the first definitions of acids and bases and is restricted to water solutions and does not include many compounds (like NH₃) which nowadays are identified as acids or bases.

Some examples of Arrhenius acids and bases are: